Flat-panel displays are becoming increasingly commonplace in today's commercial electronic devices. The flat-panel displays are finding widespread use in many new products, such as cellular phones, personal digital assistants (PDAs), camcorders, and laptop personal computers (PCs). The current generation of handheld electronics places stringent demands on their displays. The flat-panel displays in these devices are expected to be lightweight, portable, rugged, low-power and high-resolution.
One example of a flat-panel display is a display screen made with thin-film transistor (TFT) technology. TFTs, common in notebook and laptop computers, generally have a transistor for each pixel on the screen. A display is generally composed of a grid (or matrix) of picture elements (“pixels”). The collection of pixels creates an image on the display. TFTs in a display act as switches to individually turn each pixel “on” (light) or “off” (dark). The TFTs are the active elements, arranged in a matrix, on the display. Having a transistor at each pixel means that the current that triggers pixel illumination can be smaller and therefore can be switched on and off more quickly. Thus, the TFT display technology is more responsive to any changes. For example, when a user moves a mouse across the screen, a TFT display rapidly reflects the movement of the mouse cursor as compared to conventional displays.
TFT displays, however, are more susceptible to degradation over time. Particularly, a threshold voltage (VT) of a TFT tends to shift under bias stress (VT-shift). Consequently, the TFT display uniformity degrades over time due to differential aging of the TFTs employed in the pixel circuits. In order to compensate for this degradation, display manufacturers generally preset voltage values used to drive the TFTs in the TFT display at a high level that ensures optimal operability of the display over the lifetime of the display. However, setting high voltage values of the TFTs at the onset results in greater power consumption than is necessary during the early periods of the display lifetime. Additionally, presetting to high voltage values may deteriorate the operational lifetime of the display more quickly than displays utilizing low voltage values.